Housings developed for holding racks of equipment generally take the form of a tower of substantially rectangular cross-section. A number of Standards have been established over the years to define certain features of these housings, so that racks of equipment can then be designed to be held in any housing that meets a defined "Standard". One such Standard is the European Telecommunications Standards Institute (ETSI) ETSI Standard, which defines the cross-sectional dimensions of the rack, often referred to as the "footprint", the spacing of the mounting holes, etc.
A typical prior art housing is illustrated in FIGS. 1A and 1B. FIG. 1A illustrates a plan view of a typical prior art housing, whilst FIG. 1B illustrates a perspective view. As illustrated in FIG. 1A, a back wall 100 has two internal side walls 120 depending therefrom. Each internal side wall 120 is bent at its far end to form a U-shaped end portion 130, which provides the side wall 120 with increased structural rigidity.
External detachable side walls 150 are provided, which may be attached to the back wall 100 of the housing. Further, a front cover 160 may be attached to the front of the housing if desired. This front cover 160 may take the form of a detachable panel, or alternatively may be provided as a hinged door attached to the housing.
With the front cover removed, or hinged open, a rack of equipment may be inserted into the housing, and attached by a suitable fastening mechanism, for example a number of bolts, to the front faces 140 of the internal side walls 120. Due to the U-shaped sections 130 provided in the side walls 120, these side walls 120 have sufficient mechanical rigidity to retain one or more racks of equipment.
As illustrated in FIG. 1B, wiring that needs to be routed to a rack of equipment may be threaded down the gaps 170 between the internal side walls 120 and the external side walls 150, and may then be passed through appropriate openings 190 in the side walls 120 in order that they can be connected to the racks.
As is apparent from FIGS. 1A and 1B, one problem with such a prior art arrangement is that the front access to the spaces 170 containing the wiring is through a rather restricted narrow entrance 180, this narrow entrance being formed as a direct result of the U-shaped channels 130 introduced to improve mechanical rigidity. This can impede maintenance work, and/or the introduction of new wiring into the housing, particularly if a number of similar housings are located side by side, so that there is no longer the possibility of removing the side walls 150 in order to obtain side access to these wiring areas. Since Standards such as the ETSI Standard will dictate the overall dimension "X", illustrated in FIG. 1A, it is not possible merely to increase the width of the housing, in order to improve the front access to the wiring through the opening 180.
Another problem that may be exhibited when such a housing is used to retain one or more racks of electrical equipment is that of noise propagation to the components of the rack. In a typical prior art housing, such as that illustrated in FIGS. 1A and 1B, the wires may be routed via the gaps 170 between the internal side walls 120 and the external side walls 150, be passed through an appropriate opening 190, and then be directly connected to the rack of equipment. Typically, these wires may have a metallic core along which the signal passes, surrounded by an insulating portion, an outer metallic layer used to shield the inner metallic core from external noise such as electro-magnetic emissions from other equipment in the vicinity, and then an insulating surface layer. Noise may be propagated along the outer shielding layer of such wires, and hence be propagated on to the rack of equipment at the point of connection of those wires to the rack, unless some steps are taken to remove that noise prior to the wiring being connected to the rack of equipment.
A common technique used to remove such noise involves the use of a "Ferrite", this generally having a cylindrical shape, with the wiring being arranged to pass through the centre of the Ferrite. The Ferrite is manufactured of a magnetic material that has very low eddy-current loss, and hence the Ferrite can be used as a noise filter to remove noise being propagated along the outer shielding layer of the wire. However, these Ferrites will only remove noise within a particular predetermined frequency range, and hence one needs to know the frequency to be removed/filtered before an appropriate Ferrite can be chosen. Further, such Ferrites are reasonably expensive, and can also be quite bulky.
Hence, it is an object of the present invention to provide an improved housing for holding a rack of equipment, which avoids the need for Ferrites in order to inhibit the transmission of noise along the wires to the rack.